Constitutionally Dynamic Oil Well Construction Fluids–Metalloaminal Chemistry

Physical organic studies and dynamic covalent chemistry of picolyl heterocyclic amino aminals

A dynamic covalent system of the picolyl heterocyclic amino aminals has been studied. The aminals are characterized as a metastable species and easily switch to other forms via external stimuli. The solvent, temperature, acid-base and substituent effects have been examined to evaluate the dynamic covalent system. The results reveal that a more polar solvent, a lower temperature, basic conditions and an electron-withdrawing moiety contribute to the stabilities of aminals. The existence of the n → π* interaction between acetonitrile and the C[double bond, length as m-dash]N moiety makes the N-pyrimidyl imine (4c and 4d) yield higher in CD3CN. In a similar fashion, all aminals tend to convert to the corresponding hemiaminal ethers in a methanol environment. According to these findings, we successfully synthesized the following species: (a) N-2-picolylpyrimidin-2-amine 6c obtained by reduction using acetonitrile as the specific solvent; (b) a picolyl aromatic amino aminal 3e prepared from 2-pyridinecarboxaldehyde and the electron withdrawing 2-methoxy-5-nitroaniline.

Coordination Dynamics and Thermal Stability with Aminal Metallogels and Liquids

In this article, we review a dynamic covalent gel system developed as a high temperature well construction fluid. The key gel/fluid phase changes and related materials properties are addressable via the constitutional and coordination dynamics of the equilibrium and non-equilibrium molecular species comprising the material. The interplay between these species and external stimuli leads to material adaptability. Specifically, the introduction of metal ions into a non-equilibrium hemiaminal gel reverts this phase into a non-equilibrium liquid. When heated, this liquid transforms itself catalytically into the thermodynamically favoured closed-ring polyhexahydrotriazine (PHT) gel product. The temperature stability of different PHT gel formulations is evaluated as a function of the inclusion of various salts. It is possible to revert this thermodynamic PHT gel back into a liquid. This pH dependent transformation depends on the R groups linking the hexahydrotriazines (HTs) to one another. While polyethylene glycol (PEG) based PHT gels revert to liquids with water and mild protonation conditions, in comparison, polypropylene glycol (PPG) based gels require stronger acid conditions with heat, or a different more nucleophilically driven ring-opening mechanism by, for example, phosphines. The covalent dynamic chemistry in this chemical system gives way to many possible applications in addition to the high temperature solution-gelation (sol-gels) for which it has been primarily designed.